Epic Antarctic Ice-Shelf Collapse Caused by Chain Reaction

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The mysterious disintegration of a giant Antarctic ice shelf that
had been stable for millennia was caused by a chain reaction of
lakes draining on top of the ice, researchers say.

This finding suggests that other ice shelves could be vulnerable
to such abrupt collapses, the researchers said.

Scientists investigated the spectacular
2002 breakup of Antarctica's Larsen B I ce
S helf,
a vast plate of ice larger than Rhode Island that once covered
more than 1,160 square miles (3,000 square kilometers). The ice
shelf (the tongue of a glacier that floats on the ocean) had been
stable for thousands of years but crumbled into thousands of
icebergs over the course of just a few days.

Before the ice shelf fell apart, more than 2,750 lakes existed on
top of it. These "supraglacial lakes" formed as ice and snow
gradually melted over the preceding years. [ Album:
Stunning Photos of Antarctic Ice ]

"The lakes tend to pool in place, rather than running off the ice
shelf into the ocean, as the ice shelf is very flat," said study
lead author Alison Banwell, a glaciologistat the University of
Chicago.

The researchers noted that in the days right before the ice shelf
collapsed, the majority of these lakes drained. However,
scientists didn't know why.

Now, computer simulations have solved two mysteries at once —
what made the lakes disappear, and how the ice shelf broke up so
quickly.

The model analyzed the stresses the supraglacial lakes created on
the
ice shelf. The scientists discovered that the draining of
just one of these lakes down into the ice could trigger the
formation of cracks in the ice under neighboring lakes. These
cracks could, in turn, lead numerous lakes to empty, causing
fractures to arise under more lakes — a chain reaction.

"Although previous studies have suggested that the widespread
breakup of the Larsen B Ice Shelf was probably due to the
drainage of almost 3,000 surface lakes, no previous study has
explained how and why these lakes would have drained within just
a few days in order to cause such a rapid and explosive breakup
event," Banwell said. "Our suggestion that the drainage of one
single 'starter' lake can produce multiple fractures that are
able to drain hundreds of surrounding lakes through a
chain-reaction process is, therefore, of crucial importance. We
argue that it was this chain-reaction process which contributed
to the abruptness of the explosive disintegration of the Larsen B
Ice Shelf."

More breakups on the way?

If current warming trends prevail, "lake-induced breakup may
threaten other Antarctic
ice shelves and cause them to disintegrate in a similarly
dramatic way," Banwell told LiveScience.

It's important for scientists to determine the risk of Antarctic
ice-shelf collapses because these vast blocks of ice essentially
serve as dams for the glaciers flowing into them. The removal of
these buttresses causes glaciers to feed more ice to the ocean,
"which ultimately causes sea levels to rise," Banwell said. "The
next to go is likely to be the Scar Inlet, followed by the Ross
and Ronne-Filchner ice shelves." (At a recent scientific meeting,
Ted Scambos, a glaciologist with the National Snow and Ice Data
Center in Boulder, Colo.,
predicted that the Scar Inlet Ice S helf,
which is a remnant of the Larsen B Ice Shelf, would be the next
to go.)

The ultimate proof of this idea "may only come when the next ice
shelf collapses," Banwell concluded.

Banwell and her colleagues Douglas MacAyeal and Olga Sergienko
detailed their findings in the Nov. 28 issue of the journal
Geophysical Research Letters.